The present invention relates generally to golf balls. Specifically, this disclosure relates to golf balls including a highly neutralized polymer and a modifier, where the modifier changes the hardness of the highly neutralized polymer.
Golf is an increasingly popular sport at both the professional and amateur levels. Generally, mass produced golf balls should be able to meet the requirements of golfers of a wide variety of ability levels. For example, the materials used in the golf ball's construction may be chosen so as to make the golf ball more suitable for particular types of golfers.
Generally, modern golf balls are known to be made from a variety of polymer materials. The material making up a golf ball may affect the golf ball's performance characteristics in several ways. For example, the selection of the material used in a golf ball may affect the golf ball's coefficient of restitution, initial velocity off the tee, feel, durability over time, and other properties.
Suitable known materials for use in a golf ball include thermoset materials, such as rubber, styrene-butadiene copolymer, polybutadiene, cis-polyisoprene, and trans-polyisoprene. Known materials also include thermoplastics, such as ionomer resins, polyamides or polyesters, and thermoplastic polyurethane elastomers. Suitable materials also include polyurea compositions, as well as other materials.
In particular, ionomers are often used to form the various structural components of known golf balls. For example, ionomers such as Surlyn™ available from E.I. DuPont de Nemours & Company are known to be used for cover layers of golf balls. Other types of ionomers, generally referred to as highly neutralized polymers, may also be used in golf balls.
Specifically, highly neutralized polymers are known to be used as the material for a golf ball core. For example, U.S. Pat. No. 6,756,436 to Rajagopalan et al., entitled “Golf Balls Comprising Highly-Neutralized Acid Polymers” and filed Apr. 9, 2002, discloses golf balls having highly neutralized polymer cores. The disclosure of this application is hereby incorporated by reference. Other conventional highly neutralized polymers are generally disclosed in U.S. Pat. No. 7,652,086 to Sullivan et al., entitled “Highly-neutralized Thermoplastic Copolymer Center for Improved Multi-layer Core Golf Ball” and filed Feb. 3, 2006, the disclosure of which is hereby incorporated by reference.
Certain formulations of the highly neutralized polymer may affect various physical properties of the polymer material, and so may affect the play characteristics of a golf ball made from that material. For example, various highly neutralized polymers may achieve increased hardness, modulus, and resilience characteristics. These properties of highly neutralized polymers may be advantageous to golf ball covers, cores, or other structural components, in order to achieve desired play characteristics.
However, in many instances known to a person having ordinary skill in the art of golf ball manufacturing, a highly neutralized polymer may have a hardness that is higher than may be preferable. Specifically, a core made from a highly neutralized polymer may be harder than preferable to highly skilled golfers. Generally, a golf ball's “feel” may be related to the hardness of the material making up the golf ball's core. Highly skilled golfers may prefer golf balls that have a soft feel when hit by a golf club. A golf ball with a core made from a highly neutralized polymer may therefore fail to achieve a highly skilled golfer's preferred “soft feel.”
Additionally, an overly hard core may cause the golf ball to make a higher (or “harder”) than desirable sound when stuck by a golf club. Experienced golfers generally prefer their golf balls to make a low frequency sound when struck. However, a core with a high hardness may cause the sound to be of a higher frequency, which is sometime referred to by golfers as sounding “too clicky”.
Furthermore, economic considerations may also make conventional highly neutralized polymers less than ideal. Namely, the price of raw highly neutralized polymer may be significantly higher than the price of other raw materials used in golf ball constructions.
U.S. Patent Application No. 2003/0158312 to Chen, entitled “Stearic-modified Ionomers for Golf Balls” and filed on Aug. 21, 2003, attempted to address some of the above discussed issues. This patent application discloses certain types of highly neutralized polymers, where the highly neutralized polymer is blended with ethylenically unsaturated carboxylic acid present in an amount of from 5 to 25 wt percent. For example, the highly neutralized polymer is modified with relatively low amounts of a stearic acid moiety in order to achieve improved resilience for a given level of hardness or PGA Compression values. The disclosure of this patent application is hereby incorporated by reference.
U.S. Pat. No. 7,637,824 to Shindo et al., entitled “Golf Ball” and issued on Dec. 29, 2009, also addresses modification of highly neutralized polymers. This patent discloses a golf ball with a cover layer made up of a type of highly neutralized polymer having a Shore D hardness of at least 60, an unsaturated fatty acid, and a metal neutralizing agent. The unsaturated fatty acid causes the highly neutralized polymer to soften.
However, there still exists a need in the art for a golf ball that addresses the above discussed shortcomings relating to hardness, sound, and economic considerations in the context of highly neutralized polymers.